The present invention relates generally to integrated circuit designs, and more particularly to methods and apparatuses for implementing multiple electrical fuses in a fuse cell equipped with only one programming device.
Electrical fuses are often utilized for modern semiconductors. Typically, they are designed to blow when a current through the fuses exceeds a pre-determined threshold. When the fuses are programmed or “blown”, although not necessarily physically broken, they enter into a high impedance state. Electrical fuses are commonly used for making adjustments and repairs that are performed as late as after the chip is packaged. Since wirings are allowed at the two ends of the fuses, the fuses can be flexibly positioned within the chip, which is much more desirable than the conventional laser fuses as it is impossible to implement many metal layers or thick dielectrics above the laser fuses. This flexibility makes electrical fuses a desirable component for higher density memory devices.
However, conventional methods of programming electrical fuses in a memory device are not very efficient in utilizing precious silicon area and thus are costly. For example, conventional methods for programming an electrical fuse require that one programming device is assigned for each fuse. In order to program an electrical fuse, a large supply current is necessary to be directed through the fuse. In order to provide this large supply current, programming devices attached to the fuses are very large. As the number of electrical fuses increase, the number of these large programming devices also increases proportionally. The result is a very poor rate of silicon area utilization.
It is always desirable to provide an improved programming mechanism with multiple fuses to improve silicon area utilization without causing deterioration to operational performance.